In recent years, as an apparatus for supplying air suitable for an ultra-clean working space, for example, a clean room, a clean chamber, a mini-environment, or the like, which are used in cutting-edge electronics industries such as a semiconductor devices manufacturing plant, a liquid crystal display manufacturing plant, a solar cell manufacturing plant, etc., there have been already practically used a rotor type air cleaning apparatus that can be semi-permanently used by simultaneously performing the adsorption and regeneration of contaminants in air such as an ammonium component, an amine compound component, a sulfur oxide component, an organic compound component, a sodium component, a potassium component, a metal component, water, a peroxide component, etc., with an adsorbent, and said apparatus continuously removes the above molecular contaminants in air and continuously supplies a working space with clean air, and also rotor type dehumidified-air supply apparatus (desiccant) that continuously removes water in air. However, the rotor type air cleaning apparatus essentially has an inherent problem that is difficult to overcome as will be described later, so that it is not easy to bring a further cleaner air environment with a higher degree into reality. In principle, therefore, an air cleaning apparatus and a dehumidified-air supply apparatus provided with two lines of adsorbent units based on a batch type temperature swing adsorption (TSA) are the most preferred. Since, however, this type also has following difficult problems that remain to be solved, and has not yet been put to practical use.
(Conventional Batch Type Temperature Swing Apparatus)
An air cleaning apparatus based on the batch type temperature swing adsorption, as an apparatus for continuously supplying air suitable for a clean working space, generally has first and second adsorbent units (two-line systems). In the first line, cleaning and dehumidification by adsorption are performed, and in the second line, desorption of adsorbed substances and regeneration are performed. Unit portions of the apparatus that perform the above cleaning and dehumidification functions and that perform adsorbed-substances desorption and regeneration functions are required to be as compact as possible. Further, what is even more important is that the apparatus is required to have capability of being substantially free of a variation each in the flow rate, static pressure and pressure difference of supplied gas, each time when “switching of adsorption/regeneration modes” for the adsorption operation and regeneration operation is made in the first line and the second line.
In the conventional batch type temperature swing adsorption apparatus having two lines of adsorbent units, however, it all remains unsolved to provide such a compact apparatus that is also capable of controlling the flow rate variation, static pressure variation and pressure difference variation within tolerant accuracies when switching of the adsorption/regeneration modes are made. These variations at the switching time have been regarded as inevitable so long as a batch type apparatus is used.
(Selection or Switching of Adsorption/Regeneration Modes)
In the batch type temperature swing adsorption (TSA) apparatus having two lines of adsorbent units, the “selection or switching of adsorption/regeneration modes” (“selection of admission modes”) refers to the following operation. Specifically, in an operation while a treatment gas (gas to be treated, i.e., a gas such as air containing contaminants and water to be removed by adsorption) is caused to pass through the adsorbent unit in the first line to perform the adsorption operation, concurrently, a regeneration gas (which refers to a gas to be used for the desorption of adsorbed substances, water, etc., and for the regeneration of an adsorbent by heating the adsorbent) is caused to pass through the adsorbent unit in the second line, the adsorbent of the second adsorbent unit is heated for desorption and regeneration until the adsorption capacity of the adsorbent unit in the first line comes to its limit, then, the adsorbent of the second adsorbent unit is cooled and at the time when the regeneration operation is completed, the treatment gas passing through the adsorbent unit in the first line is switched to the regeneration gas, and at the same time the regeneration gas passing through the adsorbent unit in the second line is switched to the treatment gas.
In the switching operation to come thereafter, naturally, switching of adsorption/regeneration modes is made where the regeneration gas is switched to the treatment gas in the first adsorbent line and the treatment gas is switched to the regeneration gas in the second line.
FIG. 6 shows a conventional batch type temperature swing adsorption apparatus having two-line adsorbent units. It will be explained in detail below why the formation or building of a compact unit is difficult in such a conventional apparatus and why a variation in flow rate, a variation in static pressure and a variation in pressure difference are inevitable when the switching of adsorption/regeneration modes are made.
FIG. 6 shows a conventional air cleaning apparatus 200 and based on the batch type temperature swing adsorption provided with two lines of adsorbent units, each unit having honeycomb-shaped of activated carbon as an adsorbent for removing molecular organic contaminants in the air, the shaped activated carbon being stacked in a container.
(Procedures During Steady State Operation)
Treatment air flows in through a treatment air inlet 101, passes through a treatment air duct 106 via a treatment air blower 103, a treatment air filter 102 and a treatment air damper 105 and flows into a branching/confluent point T1 in a first-line duct 110 and a second-line duct 117. When the air is passed through a first-line adsorbent unit 109 to perform adsorption and when regeneration air is passed through a second-line adsorbent unit 118 to perform regeneration, an on-off value V1 on the first line side is in a valve-opened state and an on-off valve V4 on the second line side is in a valve-closed state.
Air to be treated (treatment air) flows in the treatment air duct 106, passes through the branching/confluent point T1, the on-off valve V1 and a branching/confluent point T2 and flows into first-line adsorbent units 109 (109a, 109b) connected to a first-line duct. While the air passes through the first-line adsorbent units 109a and 109b, molecular organic contaminants are eliminated, and the air flows into a supply air duct 115 through an on-off valve V2 in a valve-opened state and a branching/confluent point T4, passes through a supply air filter 128 and flows out of a supply air outlet 116 as cleaned supply air. In this state, the valve V2 is in a valve-opened state, so that on-off valves V3 and V6 are in a valve-closed state.
On the other hand, the regeneration air is sucked into a regeneration air blower 122 from a regeneration air inlet 119 through a regeneration air filter 121 and taken into the air cleaning apparatus 200. The regeneration air flows in a regeneration air duct 120, passes through a regeneration air damper 124, a regeneration air cooler or cooling unit 125 and a heater 127 and flows into a branching/confluent point T8 connected to the first-line duct 110 and the second-line duct 117.
For regenerating second-line adsorbent units 118 (118a, 118b), regeneration air passes though an on-off valve V7 in a valve-opened state, flows in the second-line duct 117 through a branching/confluent point T5 and flows into the second-line adsorbent units 118a and 118b. 
During the desorption of substances adsorbed by the second-line adsorbent units 118a and 118b, the regeneration air is heated with the heater 127. For this time period, the cooler 125 is not working or at rest. During the cooling of the second adsorbent units 118a and 118b at a elevated temperature after the desorption of the adsorbed substances, the regeneration air cooler or cooling unit 125 is operated. For this time period, the heater 127 is not working or at rest.
The regeneration air that has passed through the second-line adsorbent units 118a and 118b passes through a branching/confluent point T6 and an on-off valve V8 in a valve-opened state, further passes through a branching/confluent point T7 and flows in an exhaust air duct 113 to be exhausted out of the line through an exhaust air outlet 114. In this case, the on-off valve V8 is in a valve-opened state, and the on-off valves V4 and V5 are hence in a valve-closed state.
Further, the on-off valve V4 is in a valve-closed state, so that no regeneration air flows into the branching/confluent point T1 of the treatment air duct 106.
(Difficulties in Switching of Adsorption/Regeneration Modes)
In the above state, it is required to perform the selection or switching of the adsorption/regeneration modes of the first-line adsorbent units 109a and 109b from adsorption operation to regeneration operation and to switch the second-line adsorbent units 118a and 118b from regeneration operation to adsorption operation within a very short period of time (e.g., 0.8 second), while this switching operation is very difficult.
That is because it is required to switch the four valves (V1, V2, V7 and V8) in a valve-opened state to a valve-closed state in an instant and simultaneously switch the four valves (V3, V4, V5 and V6) in a valve-closed state to a valve-opened state in an instant and simultaneously.
In the conventional air cleaning apparatus 200 provided with the two lines of adsorbent units based on the batch type temperature swing adsorption, if clean air is to be supplied by simultaneously performing adsorption and regeneration, it is required to connect the first-line adsorbent units 109a and 109b, the second-line adsorbent units 118a and 118b and ducts in which the air flows, while preventing the inter-mixing of treatment air, supply air, regeneration air and exhaust air. It is therefore required to provide or arrange, upstream of the adsorbent units, two duct lines where treatment air and exhaust air flow, the branching/confluent point T1 for taking treatment air and distributing the air to the adsorbent units of the first line and the second line, the branching/confluent point T7 of a duct connected to the exhaust air duct 113 that leads exhaust air from the first-line duct 110 and the second-line duct 117 to the exhaust air outlet 114 and the valves V1, V4, V5 and V8 on either side of them for opening and closing duct circuits.
It is also required to provide or arrange, downstream of the adsorbent units, two duct lines where supply air and regeneration air flow, the branching/confluent point T4 connected to the supply air duct 115 that leads supply air to the supply air port 116 from the first-line duct 110 and the second-line duct 117, the branching/confluent point T8 for distributing regeneration air to the adsorbent units of each of the first and second lines, and the valves V2, V3, V6 and V7 on either side of them for opening and closing ducts.
Further, it is also required to provide or arrange the branching/confluent points T2 and T6 for the flow of regeneration air from the first-line duct 110 to the exhaust air duct 113 and from the second-line duct 117 to the exhaust air duct 113, and branching/confluent points T3 and T5 for the flow of regeneration air from the regeneration air duct 120 to the first-line duct 110 and from the regeneration air duct 120 to the second-line duct 117.
As described above, ultimately, it is required to provide or arrange, upstream and downstream of the adsorbent units 109 and 118, two duct lines each or a total of four ducts lines, a total of eight on-off valves and a total of eight branching/confluent points, and it is required to provide or arrange as many as four duct lines.
Therefore, the arrangement of very complicated and long ducts is required. The “duct” for use in a semiconductor manufacturing plant, etc., which the present invention is aimed at or directed to, is not any small pipes having a diameter of approximately 50 mm. The above “duct” refers, for example, to a duct having the cross section of a square each side of which is 500 mm long (for example, when the amount of treatment air is 100 m3/minute, a duct having the cross section of a square has dimensions of approximately 500 mm each for its flow at a rate of approximately 8 m/s).
When the above arrangement extends to a length of 30 m, the ducts alone require an occupation space of as much as 6.2 m3. When the amount of treatment air is 20 m3/minute, and when the flow rate is similarly approximately 8 m/s, the arrangement extending to a length of 30 m requires an occupation space of 1.3 m3 for ducts alone.
That is, the occupation space of ducts where air under atmospheric pressure flows is vast in reality, and in addition thereto, there are occupation spaces necessary for branching/confluent points of ducts, overlaying, crossing, curving and enlarging (reduction) of ducts, on-off valves, attaching of insulating materials, and the like, so that the occupation space of the entire apparatus is extremely large.
The above is a first reason for making it difficult to form a compact batch type temperature swing adsorption apparatus having two lines of adsorbent units. Naturally, it is clear that it is impossible to form any compact apparatus as it is, while the problem cannot be solved with ease.
Further, since the switching of the adsorption/regeneration modes requires simultaneous switching between adsorption and regeneration operations, it is required to simultaneously start the switching operations of a total of the eight on-off valves having a small pressure loss and a large aperture and simultaneously stop their operations without discontinuing the flows of treatment air and supply air, and the selection time period is required to be as small as possible (e.g., 1 second or smaller).
However, it is very difficult to switch all of the eight on-off valves simultaneously for a short period of time. And, if any one or ones of the on-off valves delays or delay slightly, there is further caused a serious problem of variation in the flow rate and pressure of the supply air.
In FIG. 6, for example, when the time for the on-off value V1 to start the switching from being opened to being closed and the time for the on-off valve V4 to start the switching from being closed to being opened delay by 0.1 second, and when the other on-off valves V5, V8, V2, V3, V6 and V7 have no delay, the flow of treatment air stops for a moment (for 0.1 second) and immediately restores itself, and a variation thereby caused in the flow rate is transmitted as such in the supply air duct 115 at a speed corresponding to the flow rate.
On the other hand, concerning a variation in pressure, a sharp variation in pressure takes place in which the pressure changes from a normal supply air static pressure to zero and restores the normal supply air static pressure after 0.1 second.
The above sharp variation in pressure is in fact transmitted in the duct at a very high speed that one skilled in the art does not expect. That is, this variation in pressure is transmitted in the supply air duct 115 at the speed of sound, that is, at a high speed of approximately 320 m/second. In reality, the eight on-off valves have different in a time period for the opening/closing operation, so that various states of variations take place in the above flow rate and pressure.
In the producing step of semiconductors, etc., it is required to supply a large amount of clean air suitable for a clean working space stably and continuously. When such variation of flow rate and pressure of supply air occurs in or during the above switching procedure, it can be a great factor which causes greatly decreasing the through-put or yield of semiconductor products. There exists thus the following serious problem; how variations in the flow rate and pressure taking various varying states caused by the switching operation, in particular the pressure variation that is transmitted at an unexpected high speed or the speed of sound, can be controlled within tolerant accuracies.
Still, another problem with the conventional apparatus of FIG. 6 is that since the air in any ducts between the eight on-off valves and between the eight branching/confluent points comes to stop flowing when the on-off valves are brought into a valve-closed state, thereby creating stagnation portions where the air stays and stagnates as it is until the valves are again brought into a valve-opened state.
For example, the duct between the branching/confluent point T6 and the branching/confluent point T1 and the duct between the branching/confluent point T2 and the branching/confluent point T1 can become stagnation portions where exhaust air, containing a high concentration of desorbed contaminants immediately after the start of regeneration, stagnates, which stagnation causes a serious problem of influencing the cleanness of supply air immediately after the start of adsorption.
As described above, the conventional batch type adsorption apparatus has a plurality of serious problems that cannot be easily solved, so that at present there is attempted another approach to the employment of continuous operation on the basis of completely different operation principles, thereby precluding the necessity of adsorption/regeneration switching modes inherent to the batch type apparatus. For example, JP2001-141274A proposes a rotor type air cleaning apparatus, and JP11-188224A proposes a rotor type dehumidified-air supply apparatus. However, these proposed apparatuses also have the following serious problems.
That is, these rotor type air cleaning apparatuses generally require, depending upon the number of adsorption rotors used, four to six air blowers since two or three rotors are used connected in series. At both upstream and downstream of the rotors, specialized hoods or covers are required in each of three sections or parts of each rotor, the adsorption process, regeneration process and cooling process. In addition to these, a filter, a damper, a valve, a heater and a cooling unit are required. Thus, the rotor type air cleaning apparatus and the rotor type dehumidified-air supply apparatus require a very large number of component units and parts.
Further, the rotor has a larger cross-sectional area than a duct connected thereto. In addition thereto, there are ducts per se, branching/confluent points of ducts, overlaying, crossing, curving or bending arranging and enlarging (reduction) of ducts and hoods for rotors, so that the rotor type air cleaning apparatus and the rotor type dehumidified-air supply apparatus inevitably have a large occupation space. In principle, with the rotor type air clearing apparatus it is difficult to further decrease the occupation space, thereby making application of them to the mini-environment system quite difficult.
Moreover, since the adsorption rotor in the rotor type apparatus rotates, the hoods in those regions, attached upstream and downstream thereof, are required to be attached close to or in vicinity of the end surface or edge face of the rotor. It is hence difficult to prevent the leakage out, leakage in and mixing of air that goes into or comes out of each rotor, such as treatment air, supply air, regeneration air, cooling air or air under treatment. In particular, it is much more difficult to remove molecular contaminants thoroughly until the concentration thereof is extremely low as is required in the semiconductor industry. There is an additional problem that since air is liable to leak from the vicinities of the rotor, thereby making contamination liable to be diffused. Furthermore, it is very difficult to realize a rotor type nitrogen-gas cleaning apparatus or rotor type humidified-nitrogen-gas supply apparatus using nitrogen gas instead of air.